.nav {
  position: relative;
  width: 100vw;
  height: 180rpx;
  z-index: 999;
}

.icon-back {
  position: fixed;
  top: 45px;
  left: 15px;
}

.title {
  color: #3F3F3F;
  font-size: 40rpx;
  font-weight: 500;
  position: fixed;
  top: 45px;
  left: 50%;
  transform: translate(-50%, 0%);
  /* 使元素在视口中居中 */
}